The Washington University Mass Spectrometry Facility has functioned as a local and regional resource for mass spectrometry since 1969, when our first instrument, and LKB-9000 was put into operation. The Facility grew to include four quadrupole GC/MS systems, acquired in 1974-1975. That growth was the result of intense utilization of the Facility by a large number of individuals mainly needing quantitative GC/MS for the analysis of stable isotope tracers in human metabolism and for quantitative measurement of biological substrates and drugs. All of these instruments were supported by data systems of our own design and construction, the commercial systems of that period being deficient in one or more of our needs. Throughout the latter period, as is still the case, we have maintained and modified our instruments, at all times having resident skills for all of our operating and developmental needs. The last GC/MS that came into the Facility was purchase in 1983 for the specific purpose of prostanoid analysis, and was necessarily set aside for the need because heavy general use often left the other instruments with background contamination, often making high sensitivity analysis impossible. We are still operating at a high level of activity (last year we logged 7453 hours of GC/MS time without the LKB, which has been retired) but now with four mass spectrometers that are 12-13 years old. The original instruments are now suffering increasing failure and consequent down-time, occupying Facility staff in repair activities that take away from other grant- supported work. We are therefore seeking funds to replace one of our original quadrupole mass spectrometers. We are asking for support to purchase a current-model quadrupole instrument, with the manufacturer's data system, the latter to avail ourselves of the control capabilities that are a part of today's commercial equipment.